1. Field of the Invention
The present invention relates broadly to measuring haze of materials, such as coatings or films. More particularly, the present invention and associated methods are directed to high throughput methodologies for screening a plurality of materials in order to efficiently and rapidly ascertain characteristic-properties of materials, in particular, haze.
2. General Background and State of the Art
Materials display a wide range of characteristics that depend upon the various components that go into or make up particular materials. An exemplary, abbreviated list of the various characteristics that a material may display includes mechanical, thermal, chemical, electrical and optical properties. Many of these categories of characteristics may be further subdivided into other, more specific categories. For example, a plethora of additional descriptive categories fall within the more general category of optical characteristics. These include luminance, color, illuminance, brightness, transmission and absorption of various wavelengths of energy, reflectance and haze. The present invention is concerned with providing a novel and improved apparatus and associated methods of use that provides the expeditious determination of haze characteristics of a plurality of materials differing in their compositions.
Light that impinges upon materials may be reflected, absorbed, scattered or transmitted. Accordingly, the amounts and quantities of the various components that make up a material affect the manner in which light behaves when falling onto and/or through it. For example, certain components may scatter light more readily than other components. Similarly, other components of the materials may impart certain chromatic characteristics that absorb or reflect light in a manner, for example.
Certain specific characteristics, some of which have been previously mentioned, may be especially critical for a particular use or function of a material. For example, the haze characteristics of various materials or compounds are an important aspect of the design of many products. Haze is defined by the American Society for Testing and Material as xe2x80x9cthe scattering of light by a specimen responsible for the reduction in contrast of objects viewed through itxe2x80x9d (ASTM D 1003-97).
The importance of the haze characteristic of various materials is the focus of much research and development in many industries. For example, the manufactures of various glasses and other light transmitting materials vary and optimize the optical properties of their products commensurate with their intended applications. Windshields, mirrors and other parts utilized in, the automobile manufacturing industry are continually being redesigned and optimized in regards to their various optical characteristics. In some instances, windows, of automobiles may contain, as part of their assembly, coatings or compounds on the surface of the windows, sandwiched in laminated glass sheets or within the glass proper, that are designed to reduce penetration of the UV portion of the light spectrum. This is in order to attenuate the bleaching effects of these wavelengths on fixtures found within the automobile""s interior, for example.
Similarly, manufacturers of eyewear, photographic lenses, windows, CRTs, and light filters, as well as other products, have an interest in the manner in which their products interact with light. In many instances, this light interaction provides a particular protective and/or functional role. In the case of eyewear, manufactures must provide lenses that blocks UV radiation while at the same time having an upper limit to the haze of the lens, in order to provide users with clear images when the eyewear is worn. Similarly, photographic lenses may have filters placed between them and subjects of interest in order to impart a photographic effect. The haze characteristics of these filters play a significant role in the way in which the subject is captured and ultimately portrayed in the final image.
These and other examples make clear that haze is an optical property that has relevance in wide ranging fields. The prior art standard of measuring haze utilizes a Gardner Haze Meter. In this prior art methodology, the amount of light transmitted through a material and the amount of light scattered by the same material are utilized in an equation wherein the ratio of scattered to the total amount of light that comes through the material results in a haze value.
The prior art instrumentation for assessing the haze of various materials is limiting in a number of significant aspects. Prior art methodologies are slow, often requiring a substantial amount of time, one minute or more, to assess the haze of a single material. As one skilled in the art will appreciate, this rate of material assessment results in a limitation of the amount of materials that may be tested for haze characteristics over a given amount of time. While many hundreds of materials may be formulated utilizing automated means in a research and development laboratory, the bottleneck created by the limited number of samples that may be tested efficiently presents an area of major concern.
Therefore the present invention provides an apparatus and methods that greatly increase the rate at which material may be screened for haze characteristics. In conjunction with combinatorial chemistry methods that produce hundreds, even thousands of new materials per day, the present invention overcomes the previously stated disadvantages. The present invention provides a high throughput screening method and apparatus for haze that is capable of efficiently screening a plurality of materials. In an exemplary configuration, the present invention provides users with the ability to screen 750 samples of materials per hour. This provides a concomitant increase in the rate of discovery of materials that display particular haze characteristics, as well as determining the haze of newly formulated material in general.
The present invention provides users with the capability of measuring the haze of a plurality of sample materials disposed upon a substrate in an array configuration. An illustrative method, in accordance with the present invention includes disposing upon a substrate a plurality of materials utilizing a multi-well apparatus comprising an apertured top layer placed upon a bottom, substrate layer in order to form a plurality of material receiving wells. Material to be characterized is placed into the material receiving wells and processed. Material may be deposited into the material receiving wells by various techniques, including, but not limited to, pipettes, drip nozzles or sprayed, for example, when the materials are in liquid form. These techniques may also be automated. Exemplary processing of the material may include drying and centrifugation of the assembly in order to flatten the materials in the wells upon the substrate. Once processed, the apertured top layer is removed, exposing the bottom substrate layer with the material now disposed in an array. The array of samples may be formed by other techniques.
Both layers can be flexible, with the second or bottom layer being detachable from the overlying first layer, as previously mentioned. Such an apparatus can be made of disposable material, thus providing a cost-effective, efficient and reliable means of making and testing numerous formulations of material for haze characteristics.
The present invention utilizes a novel method of determining the reduction in contrast of a target in order to determine the haze of material. A target is provided having a background with indicia disposed upon it. The contrast of the indicia against the background is then determined. The target is next viewed through a haze calibration filter having a pre-selected haze value. The reduction in contrast, as viewed through a haze calibration filter, between the background and indicia is noted. The contrast values of the target as viewed directly and as viewed through the calibration filter, are utilized to calculate a haze calibration factor. The haze calibration factor will then be utilized in subsequent calculations to determine the haze of each material disposed in the array configuration.
After determining the haze calibration factor, the target is then viewed through the array of material disposed upon the substrate. At each location where sample material is disposed, the reduction in contrast between the background and indicia comprising the target, as viewed through the material on the substrate, is determined for every sample of the material in the array. These contrast values will comprise part of the equations utilized in order to determine the haze of each material. In this exemplary configuration, with a plurality of sample materials disposed upon a substrate, the substrate itself contributes a component to this contrast reduction and thus the initial calculated haze value of the material. This substrate haze component must be determined in order to obtain the corrected or xe2x80x9ctruexe2x80x9d haze value of the material alone.
Therefore, the target is also viewed through the substrate material itself and the contrast between the background and indicia of the target is determined, as viewed through the substrate. This contrast, in addition to the haze calibration factor previously determined, is utilized to calculate haze of the substrate alone.
The haze of the samples of material disposed in an array on the substrate is then calculated by subtracting the haze value of the substrate from the initial haze value calculated for the sample material that is disposed upon the substrate. This is carried out for each of the plurality of sample material disposed upon the substrate. The values may be entered into a spreadsheet that is configured to efficiently and rapidly determine the haze of a plurality of materials. A more detailed description of the exemplary methods utilized by the present invention is provided below.
In accordance with one aspect of the invention an imaging device such as a video or still camera may capture images of an array of samples and underlying target which are appropriately illuminated, as part of the high throughput haze measuring system.
Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principals of the present invention.